The field of the invention relates generally to steam generation systems and, more particularly, to systems and methods for use in controlling the operation of steam generation systems.
At least some known steam generation systems, such as combined-cycle power generation systems, may include at least one heat source, such as a gas turbine engine, at least one steam boiler, such as a heat recovery steam generator (HRSG), and at least one steam process or a steam turbine engine (ST). Exhaust gases from the gas turbine engine can be channeled to the HRSG, wherein energy from the exhaust gases is utilized to produce steam. The steam can then be channeled to the steam process or the steam turbine engine for use in generating power therefrom. Some combined-cycle power plants can be configured with multiple gas turbine engines and multiple associated HRSGs, wherein one or more of the gas turbine engines may be coupled in flow communication to at least one of the HRSGs, and at least a single steam turbine engine or a steam process that can utilize steam generated by any or all of the HRSGs. The combined cycle power generation system can be operated at a lower power output by utilizing a single gas turbine and its associated HRSG(s) together with the steam turbine engine. If a higher power output is desired, additional gas turbine engines and their associated HRSGs may be started and operated, wherein the steam from additional HRSGs is blended with steam from the existing HRSG(s) thereby providing increased steam flow to the steam turbine engine or the steam process.
At least some HRSGs may be a multi-stage HRSGs that use heat channeled from exhaust gases from the gas turbine engine. The HRSG generates progressively lower grade steam in each successive boiler stage, wherein the steam is channeled from the HRSG to the steam turbine engine. More specifically, known HRSGs are capable of generating relatively high pressure steam in a high pressure portion of the HRSG. After heat is removed from the gas in the high pressure stage, the gas is then channeled to an intermediate pressure stage to generate an intermediate pressure steam and the gas is then channeled to a low pressure stage of the HRSG to generate a low pressure steam. The conditions of the high pressure, intermediate pressure and low pressure steam from the HRSG may be adjusted to be suitable for admission into the high pressure (HP), intermediate pressure (IP) and low pressure (LP) portions of the steam turbine engine (respectively).
Blending steam flows from multiple HRSGs and/or multiple sections of one HRSG can be a difficult operation. Such steam blending requires skilled combined-cycle plant operators to properly control the various valves, attemporators, steam drums and other equipment associated with the HRSGs and steam turbine engine to minimize process disturbances. Examples of process disturbances include improper blending, which causes drum levels to change rapidly and/or pressures and temperatures of the steam to change in an undesirable manner. Continued operation with such process disturbances can force the shutdown of the power generation system, depriving the utility of a power supply and/or causing the utility to incur undesirable costs. Moreover, the process disturbances can cause damage to the HRSG and/or can lead to a premature failure of the HRSG and/or the power generation system.